Sources of powdery mildew resistance in barley landraces from morocco

SUMMARY

A total of 44 accessions of barley landraces fromMorocco were screened for resistance to powderymildew. Nineteen of the tested landraces showed resis-tance reactions and 45 lines were selected. Sixteen ofthese lines were tested at the seedling stage with 17, andanother 29 lines with 23 differential isolates of powderymildew respectively. Six lines (170-1-3, 172-3-2, 173-1-2, 181-3-5, 201-3-2, 201-3-3) were identified that haveresistance to all the prevalent European powderymildew virulence genes. It was postulated that 3 differ-ent resistance alleles (Mlat, Mla6, and Mla14) are pre-sent in the tested lines either alone or in combination.Among the tested lines 8 (18.0%) had one specific genefor resistance and 37 (82.0%) had a combination of dif-ferent genes for resistance. Among specific resistancealleles the most common was Mlat whose presence waspostulated in 20 (44.4%) of the tested lines. The distri-bution of reaction type indicated that about 79.0% ofall reaction types observed were classified as powderymildew resistance (scores 0, 1 and 2). The majority(65.0%) of resistance reaction types observed in thetested lines was intermediate reaction type 2. The use ofnew effective sources of resistance from Moroccan bar-ley landraces for diversification of resistance genes forpowdery mildew in barley cultivars is discussed.

Key words: barley landraces, Erysiphe graminis f.sp.hordei, genetic resources, Hordeum vulgare, mildew re-sistance.

INTRODUCTION

Barley (Hordeum vulgare L.) is widely grown inmany major production regions of the crop around theworld and is often attacked by the barley powderymildew fungus (Erysiphe graminis DC. f.sp. hordei EmMarchal - synamorph Blumeria graminis DC. Golovin

Correspond to: J.H. CzemborFax: 022.7254714E-mail: [email protected]

ex Speer f.sp. hordei). The primary effect of barleypowdery mildew is reduced yield, which can reach upto 20% in Europe and 30% in North Africa (Rasmus-son 1985; Corazza 1991; Zine Elabidine 1992; Ceccarel-li et al., 1995). In addition, powdery mildew is loweringquality characteristics such as 1000-kernel weight. Thisreduction in quality is particularly detrimental for malt-ing barley (Griffiths, 1984; Rasmusson, 1985; Balkema-Boomstra and Masterbroek, 1995).

Powdery mildew on barley is one of the most clearlycharacterized systems of host-pathogen genetic interac-tions. Since 1907, when Biffen started studying the ge-netics of barley resistance to powdery mildew, morethan 100 mildew resistance alleles have been identified.In Europe, the use of specific resistance genes to controlbarley powdery mildew began in the 1930s with thework of Honecker. Since that period, barley breedershave used such resistance alleles as Mla6, Mla7, Mla9,Mla12 and Mla13 belonging to the Mla locus and the re-sistance alleles Mlk, Mlg, MlLa, Mlh and Mlra. Many ofthese alleles derived from the barley landrace popula-tions from West Asia, Ethiopia and North Africa (Biff-en, 1907; Honecker, 1938; Brown and Jørgensen; 1991Jørgensen, 1994). However, virtually all of these geneswere gradually overcome by virulent races about 5 yearsafter cultivars containing them were used on a largeacreage. Exceptions to this are cultivars with Mlo resis-tance and the Ml(La) resistance gene. The Ml(La) resis-tance gene have been effective for more than 10 years(Munk et al., 1991). Despite the fact that since 1979 Mloresistance has been deployed in many barley cultivarsthroughout Europe, there is no known virulence for mlogenes (Atzema, 1998; Czembor and Czembor, 1998).

In the nineteenth century, a few outstanding farm-ers, landowners and scientists (e.g. Knight in England,Strampelli in Italy, Janasz in Poland, Vilmorin inFrance) started selecting attractive plants from popula-tions of crop landraces based upon their phenotypicvariation (Simmonds, 1987; Janasz, 1893; Bianchi,1995; Zeven, 1996). However, in this activity often onlyone line was selected as a new cultivar and the landracefrom which it was selected was no longer maintained.This caused great genetic erosion in major crops

Journal of Plant Pathology (2000), 82 (3), 187-200 Edizioni ETS Pisa, 2000 187

RESISTANCE TO POWDERY MILDEW IN BARLEY LANDRACES FROM MOROCCOJ.H. Czembor

Plant Breeding and Genetics Department, Plant Breeding and Acclimatization Institute, Radzikow, 05-870 Bøonie, Poland

(Brush, 1992; Hammer et al., 1996). The subject of con-servation of landraces for the first time was discussed atthe Agriculture and Forestry Congress at Vienna in1890 but without results. In 1927, 37 years later, duringthe International Agricultural Congress in Rome, it wasrecommended that participants should start to organizethe conservation of landraces in their native countries(Zeven, 1996, 1998).

There exist many examples of the successful use oflandraces to solve breeding problems including lack ofsufficient resistance to diseases (Perrino, 1995; Hintum,1996; Hodgkin, 1998). This is possible because lan-draces of major crops including barley are available inGene Banks. The total number of barley accessionsworldwide is estimated to be about 280,000 (Knüpfferand Hintum, 1995). Barley breeders are constantly us-ing these genetic resources including sources of resis-tance to powdery mildew. Most powdery mildew resis-tance genes used in modern cultivars of barley are fromlandraces maintained in Gene Banks. Most of these lan-draces originated from West Asia, Ethiopia and NorthAfrica including Morocco (gene Mlat – resistance Atlas)(Czembor, 1976; Jørgensen, 1994; Czembor, 1996; Jør-gensen and Jensen, 1997).

The high level of crop diversity, including barley, ob-served in the Mediterranean Sea region lead Vavilov in1926 to propose this region as one of the major centersof crop origin (Vavilov, 1926; Perrino, 1988; Williams,1988; Valkoun et al., 1995). In the most widely accept-ed theory, postulated in 1885 by Körnicke and Werner,barley was derived from its wild ancestor Hordeumspontaneum C. Koch when Neolithic men selectedspikes with tough rachis (Körnicke and Werner 1885;Zohary and Hopf 1988; Ladizinsky 1998). Most proba-bly it happened in the Zagros Mountain region (west-ern Iran). The original area of Hordeum vulgare L. culti-vation was the Fertile Crescent (a term coined by JamesBreasted in 1916 which refers to a crescent-shaped re-gion of rich farmland that stretched, in ancient times,from the Mediterranean Sea to the Persian Gulfthrough the Tigris and Euphrates valley) (Zohary andHopf, 1988; Nesbitt, 1995; Willcox, 1995). Recently,the discovery of wild barley in Morocco has been re-ported (Molina-Cano and Conde, 1980; Molina-Cano etal., 1982). This finding suggests that North Africa maybe the possible center of origin of cultivated barley andthat it may be a multicentric crop, domesticated alongthe Mediterranean basin (Molina-Cano et al., 1987;Moralejo et al., 1994; Molina-Cano et al.,1999). Takingthis into account, barley landraces collected from Mo-rocco may be a rich source of new genes for resistanceto powdery mildew due to their high degree of diversifi-cation resulting from the long coevolution with popula-

tions of pathogen.The aim of the present investigation was to identify

powdery mildew resistance genes in lines selected frombarley landraces from Morocco.

MATERIALS AND METHODS

Plant materials. Seed samples of forty four H. vul-gare L. landraces were kindly provided by Dr. J. Valk-oun (International Center for Agricultural Research inthe Dry Areas – ICARDA, Aleppo, Syria). They werecollected in Morocco during May, June and July in1985 (ICARDA collection code MAR85). All of themwere of a spring growth type, had six row heads andcovered kernels. Generally under Polish conditions,they had low resistance for lodging and were intermedi-ate in heading date.

Pathogen. Thirty-five isolates of E. graminis f.sp.hordei Em Marschal were used (Table 1). They camefrom the collections in the Risø National Laboratory,Roskilde, Denmark; Danish Institute for Plant and SoilScience, Lyngby, Denmark, Edigenossische TechnischeHochschule – ETH, Zurich, Switzerland kindly provid-ed by Dr. H.J. Schaerer (ETH, Zurich, Switzerland)and IHAR Radzików, Poland. The isolates were chosenaccording to the virulence spectra observed on the ‘Pal-las’ isolines differential set (Kølster et al., 1986), kindlyprovided by Dr. L. Munk (Royal Agricultural and Vet-erinary University, Copenhagen, Denmark). They werepurified by single pustule isolation, maintained andpropagated on young seedlings of the cultivar‘Manchuria’ (CI 2330). This was carried out in green-house isolation rooms. Isolates were tested frequentlyon host differentials to assure their purity throughoutthe experiment.

Disease assessment. After 8-10 days of incubation,the infection types were scored according to a 0-4 scaledeveloped by Mains and Dietz (1930) (Table 2). Theseedlings were classified into susceptible or resistantgroups. Plants scoring 0-2 were included in the resistantgroup and plants scoring 3 and 4 were included in thesusceptible group.

Resistance tests. This investigation was carried outduring 1996-99 at IHAR Radzików, Poland. In winter1996/97 about 30 plants per landrace were evaluated inthe greenhouse with the R 303 isolate of E. graminisf.sp. hordei. R 303 represented the most avirulent iso-late available allowing the expression of a maximumnumber of resistance genes. The cultivar ‘Manchuria’was used as a susceptible control.

188 Barley landraces from Morocco Journal of Plant Pathology (2000), 82 (3), 187-200

Journal of Plant Pathology (2000), 82 (3), 187-200 Czembor 189

Dif

fere

ntia

l se

tIs

olat

es1

23

45

67

89

1011

1213

1415

1617

Gen

e58

-74

59-1

159

-12

63-1

A6

D 1

7G

ER

63

Pal

las

Mla

84

44

44

44

44

44

44

44

44

P1M

la1

04

04

44

40

00

00

00

00

0P2

Mla

31

00

00

00

00

00

00

00

00

P3M

la6

,Mla

140

00

00

00

44

40

40

44

04

P4A

Mla

7,M

lk,?

44

44

02

00

20

42

22

41

2P

4BM

la7

,?4

44

41

10

02

24

44

24

22

P6M

la7

,MlL

G2

44

44

00

01

20

44

42

41

2P7

Mla

9,M

lk4

40

40

00

00

04

00

00

00

P8A

Mla

9,M

lk4

40

40

00

00

04

00

00

00

P8B

Mla

94

40

40

00

00

04

00

00

00

P9M

la10

,MlD

u24

44

40

04

00

04

00

12

40

P10

Mla

120

00

40

04

00

00

24

44

40

P11

Mla

13,M

l(R

u3)

42

04

00

00

00

04

40

40

0P

12M

la22

44

40

44

44

44

04

44

40

4P

13M

la23

24

11

11

11

21

22

12

12

2P

14M

lra

44

44

04

44

44

40

04

44

4P

15M

l(R

u2)

34

44

42

42

24

22

04

44

2P

17M

lk4

44

40

22

22

04

02

22

22

P18

Mln

n4

44

44

44

44

44

34

44

44

P19

Mlp

20

22

22

22

12

22

22

22

2P

20M

lat

20

22

42

22

22

42

22

22

2P

21M

lg,M

l(C

P)4

44

40

00

44

40

44

00

00

P22

mlo

50(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)3

30(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)P

23M

l(L

a)2

44

43

23

22

33

24

34

44

P24

Mlh

44

44

04

44

04

44

44

44

4

Tab

le 1

.Diff

eren

tial i

sola

tes

used

and

thei

r in

fect

ion

type

s on

‘Pal

las’

diff

eren

tial s

et.

(con

tinu

ed)


Pal

las

Mla

84

44

44

44

44

44

44

44

44

4P1

Mla

10

00

00

40

00

40

00

04

40

0P2

Mla

34

00

00

40

00

00

40

40

00

0P3

Mla

6,M

la14

40

00

40

00

04

04

44

44

44

P4A

Mla

7,M

lk,?

24

00

02

24

04

42

04

44

44

P4B

Mla

7,?

24

00

02

24

04

42

04

44

44

P6M

la7

,MlL

G2

04

00

01

04

04

40

02

12

44

P7M

la9

,Mlk

14

40

04

00

00

00

00

00

40

P8A

Mla

9,M

lk1

44

00

40

00

00

00

00

04

0P

8BM

la9

44

40

04

00

00

00

00

00

40

P9M

la10

,MlD

u20

44

40

44

40

44

00

44

44

4P

10M

la12

00

00

04

44

04

04

04

44

24

P11

Mla

13,M

l(R

u3)

00

40

00

04

00

00

00

44

04

P12

Mla

224

00

04

40

40

04

44

04

40

0P

13M

la23

12

21

12

21

12

22

22

21

12

P14

Mlr

a4

44

34

44

44

44

44

44

44

4P

15M

l(R

u2)

24

22

22

24

44

44

44

44

44

P17

Mlk

24

40

14

24

24

40

24

44

44

P18

Mln

n4

34

04

44

44

44

04

44

44

2P

19M

lp2

22

02

22

22

22

22

22

42

0P

20M

lat

24

20

22

22

22

24

22

44

22

P21

Mlg

,Ml(

CP)

04

43

44

44

44

44

04

44

44

P22

mlo

50(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)0(

4)P

23M

l(L

a)2

23

34

44

44

42

44

44

44

4P

24M

lh4

44

34

40

44

04

44

44

44

4

Tab

le 1

.Diff

eren

tial i

sola

tes

used

and

thei

r in

fect

ion

type

s on

‘Pal

las’

diff

eren

tial s

et.

Nineteen of the tested total 44 landraces showed re-sistance reactions (Table 3). From 1 to 5 resistant plantsper each landrace were grown in the greenhouse to ob-tain their seed. Forty-five single plant lines were creat-ed. Sixteen of these lines were tested with 17 isolates ofpowdery mildew during winter 1997/98 (Table 4). An-

other 29 lines were tested with 23 isolates during winter1998/99 (Table 5). Both of these testings were conduct-ed in the IHAR Radzików greenhouse. The plants weregrown with 16 h light and 16-22oC range of tempera-ture. The inoculation was carried out when plants were10-12 days old by shaking or brushing conidia from dis-eased plants. After 8-10 days of incubation, the diseasereaction types shown by seedlings were scored.

Postulation of resistance alleles. Hypotheses on thespecific resistance genes present were made by compar-ing the reaction spectra of the tested lines with those ofdifferential lines. The lines with the same reaction spec-tra for all isolates were classified in the same group.Identification of resistance genes was made by eliminat-ing resistance genes not present in tested lines. Thenext step was to determine the postulated and possibleresistance genes. It was done on the basis of the genefor gene hypothesis. When a compatible reaction(scores 3 and 4) was observed with one given isolate, itmeant that the cultivar did not possess the resistance al-leles for which the isolate was avirulent. Incompatiblereactions (scores 0-2) with isolates possessing only oneavirulence allele among the remaining possible resis-tance alleles made it possible to postulate that thematching resistance allele was present (Flor, 1956;Czembor, 1996).


Table 2. Description of infection types and codes used(Mains and Dietz, 1930).

Infection type Macroscopic symptoms

0 no visible symptoms (immunity)

1 necrotic flecks, usually minutechlorosis often presentno mycelial growth. No sporulation(hypersensitivity)

2 necrotic flecks, often with chlorosisreduced mycelial growth. No or scarcesporulation

3 necrotic flecks or small necrotic areasfrequent chlorosismoderate mycelial growth, moderatesporulation

4 profuse sporulation of well developedcolonies and sometimes green islands

IHARnumber

ICARDAnumber

Altitude Province Site

163166169170171172173174178179181182184189190198199201202

ICB 31864ICB 31867ICB 31870ICB 31871ICB 31872ICB 31873ICB 31874ICB 31875ICB 31879ICB 31880ICB 31882ICB 31883ICB 31885ICB 31890ICB 31891ICB 31899ICB 31900ICB 31902ICB 31903

0700030004500500050006000600065006000450070012001250060006000900110014001300

Tiznit

Tiznit

TiznitTiznit

Ourzazate

OurzazateTiznitTiznit

Merekht, 20km S of Tiznit2-3km S of FaskOua-Bell oasis10km S of TigganTigane oasisTougria oasis, near AzzargazzaneTata town, INRA StationTata town, domestic gardenTrhite oasisOued MellahAlougum OasisAit Abdelah, by Ouednear Bleida, by OuedTamgrout, Oued DreaTagounite, Oued DreaOuriz, Oued DraaOurzazateImitek between Dades and TinerhirTimadriouine, near of Imiter

Table 3. Site of collection of 19 barley landraces from Morocco showing resistance to powdery mildew.


IHA

Rnu

mbe

rIs

olat

esP

ostu

late

dre

sist

ance

alle

les

Pos

sibl

e al

lele

s1

12

46

89

1112

1415

1617

1819

2021

24

58-7

459

-11

63-1

D 1

7G

EH

L 3

/5JE

H11

MH

1R

13C

R 6

3R

71/

1R

86.

1R

189

R 2

61R

275

R 3

03R

y 4d

169-

2-5

22

02

42

04

24

24

22

20

2+?

2M

la6,

Mla

14

170-

1-3

02

02

22

02

22

22

22

20

2+?

170-

2-2

04

24

44

02

01

20

24

12

2+?

172-

1-4

02

01

42

00

01

00

42

20

2+?

172-

3-2

02

12

21

02

21

12

02

20

2+?

173-

1-2

20

11

01

02

00

00

00

20

0+?

174-

3-2

22

02

42

04

42

02

02

41

2+?

174-

2-2

02

24

44

04

24

22

42

42

4+?

178-

1-4

42

22

42

04

44

44

42

22

4+?

178-

3-1

42

24

22

42

22

22

24

12

2+?

Mla

t

189-

3-4

02

24

21

42

22

42

22

22

4+?

Mla

t

198-

1-5

22

22

21

42

22

22

24

22

4+?

Mla

t

199-

1-3

22

22

22

22

22

21

24

22

4+?

Mla

t

201-

3-2

22

12

11

12

02

21

12

11

2+?

Mla

6, M

la14

, M

lk

201-

2-2

22

22

22

42

22

12

24

22

2M

lat,

+?

202-

1-1

12

22

21

20

22

22

24

22

2M

lat,

+?

Tab

le 4

.Res

ista

nce

alle

les

and

infe

ctio

n ty

pes

of 1

6 lin

es to

infe

ctio

n by

17

isol

ates

of E

. gra

min

is f.

sp. h

orde

i.

1 R

esis

tanc

e al

lele

s w

hich

wer

e no

t elim

inat

ed fr

om th

e re

actio

ns o

f sus

cept

ibili

ty a

nd c

ould

not

be

conf

irm

ed w

ith th

e re

actio

ns o

f res

ista

nce.

2U

nide

ntifi

ed r

esis

tanc

e al

lele

, not

pre

sent

in th

e ‘P

alla

s’ is

olin

es s

et.

Journal of Plant Pathology (2000), 82 (3), 187-200 Czembor 193IH

AR

num

ber

Isol

ates

Pos

tula

ted

resi

stan

ce a

llele

sP

ossi

ble

alle

les1

13

45

710

1113

1821

2223

2526

2728

2930

3132

3334

3558

-74

59-

1263

-1A 6

Em

A30

HL

3/5-

1JE

H11

MH

1-2

R 189

R 303

Ru

3T

R2

En1

/A1

R30

3.1

E 9259

-11

.1SZ

/C

10R

a7

Ra

9R

a10

Ra

13R

a16

Ra

22

163-

2-1

22

14

22

42

22

12

22

22

42

24

42

2M

lat

163-

2-5

42

24

22

42

22

02

12

24

42

24

42

2+?

2M

lat

166-

3-1

24

20

24

24

10

41

22

22

12

22

22

1+?

169-

1-2

02

04

44

04

40

40

04

44

44

44

44

4+?

2

169-

2-1

00

00

44

04

40

40

00

40

44

44

24

4M

la6,

Mla

14,

+?

170-

1-4

12

20

22

24

20

20

22

22

42

24

22

2M

lat,

+?

170-

3-4

22

22

22

22

20

20

02

22

42

24

42

2M

lat,

+?

170-

5-5

22

24

22

42

22

22

12

22

42

44

42

2+?

Mla

t

171-

2-1

20

04

22

22

22

20

02

22

22

22

24

Mla

t, +

?

172-

3-5

02

02

22

42

20

20

02

22

42

24

42

2M

lat,

+?

174-

1-4

22

24

22

02

22

22

22

40

42

24

42

2M

lat,

+?

179-

2-1

22

24

22

42

22

22

24

44

42

24

42

2+?

Mla

t

181-

3-5

22

22

22

02

12

20

22

22

22

22

20

0+?

182-

1-1

22

22

22

42

22

22

22

22

42

24

42

2M

lat,

+?

182-

2-1

22

22

42

42

22

22

22

22

42

24

42

2M

lat,

+?

182-

3-2

22

24

22

42

22

22

22

22

42

24

42

2M

lat

182-

4-3

22

24

22

42

22

22

22

22

42

24

42

2M

lat

184-

2-1

22

24

22

42

22

22

22

42

44

42

2+?

Mla

t

184-

2-2

22

24

22

42

22

12

22

22

42

14

41

2M

lat

189-

1-1

22

24

22

42

22

22

02

22

42

24

22

2M

lat,

+?

189-

2-1

22

42

22

22

22

22

22

22

22

42

42

Mla

t, +

?

189-

3-3

22

24

22

42

22

22

22

22

42

24

42

2M

lat

190-

3-2

22

24

22

42

22

22

22

22

42

24

42

1M

lat

198-

1-3

22

24

02

42

22

20

22

22

42

24

42

2M

lat,

+?

199-

2-1

22

24

22

42

22

22

22

24

22

44

22

Mla

t

201-

2-3

22

24

22

42

22

22

22

22

42

24

42

2M

lat

201-

3-3

12

00

22

22

21

22

22

22

22

22

22

2+?

Mla

t

202-

1-2

42

24

22

42

22

22

22

22

42

24

42

2+?

Mla

t

202-

2-1

42

22

22

22

20

20

02

42

42

24

42

2+?

Mla

t

Tab

le 5

.Res

ista

nce

alle

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and

infe

ctio

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pes

of 2

9 lin

es to

infe

ctio

n by

23

isol

ates

of E

. gra

min

is f.

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i.

1 R

esis

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e al

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s w

hich

wer

e no

t elim

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ed fr

om th

e re

actio

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f sus

cept

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ould

not

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pre

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e ‘P

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et.

RESULTS

All 45 tested lines possessed a resistance allele or al-leles for powdery mildew of barley (Table 4, 5). Howev-er, only 6 lines (170-1-3, 172-3-2, 173-1-2, 181-3-5, 201-3-2 and 201-3-3) originating from 5 landraces (170, 172,173, 181 and 201) were resistant to all isolates used.One of these lines (173-1-2) showed reaction type 0 andthe other 5 lines showed reaction type 2 for most iso-lates used respectively. The distribution of reaction typereadings indicate that 79% of all reaction types ob-served were classified as powdery mildew resistance(score 0, 1 and 2) (Table 6). The majority (65.0%) ofresistance reaction types observed in tested lines was in-termediate resistance reaction type 2. Thirty-six lines(80.0%) had scores 2 and 3 lines (6.6%) had score 4 formore than 50% isolates used respectively.

In 24 (53.3%) tested lines it was impossible to deter-mine which specific gene or genes for resistance arepresent (Table 4, 5). Most probably these lines pos-sessed alleles not present in the ‘Pallas’ isoline differen-tial set. In 13 (30.0%) lines the presence of unknowngenes in combination with specific ones were detected.The distribution of reaction type readings indicate theminimum number of genes involved because differentgenes for resistance may condition different reactiontypes. Based on this assumption, it may be concludedthat most tested lines had many genes for resistance. Itwas postulated that 3 different resistance alleles (Mlat,Mla6 and Mla14) are present in the tested lines eitheralone or in combination. Among tested lines 8 (18.0%)had one specific gene for resistance and 37 (82.0%) hada combination of different genes for resistance. AllelesMla6, Mla14 were postulated to be present in line 169-2-1. The most common resistance allele in tested lineswas Mlat. This allele was present in 20 (44.4%) testedlines.

DISCUSSION

Powdery mildew is now one of the most commonand most widespread disease of barley. However for along time this disease was not important for barley pro-duction (Honecker, 1938; Wolfe and Schwarzbach,1978). The first devastating epidemic of barley powderymildew was observed in Europe on winter barley in1901 and on spring barley in 1903 (Wolfe andSchwarzbach, 1978). It happened at the advent of mod-ern agricultural methods such as the large scale cultiva-tion of uniform varieties, the use of high crop densitiesand the application of nitrogen fertilizers (Wolfe andSchwarzbach, 1978; Wolfe, 1984). The main means of

controling powdery mildew are fungicides and growingof resistant varieties. However, future strategies for thecontrol of powdery mildew will have to focus increas-ingly on ecologically acceptable methods as the use ofany chemicals (pesticides, fungicides, herbicides, andmineral fertilizers) in agriculture is increasingly criti-cized in many developed countries. Such a method isbreeding for resistance. This method is considered alsoas relatively inexpensive and convenient for the farmerbecause the use of fungicides requires investment inmachinery, labor and special training (Czembor andGacek, 1990; Gullino and Kuijpers, 1994; Czembor andGacek, 1995; Brown, 1996; Jacobsen, 1997).

However breeding barley for resistance to powderymildew is faced with a highly mobile pathogen, whosegene-pool forms an almost infinite source of geneticvariation (Müller et al., 1996; O’Hara and Brown, 1997;Hovmøller et al., 2000). A number of genes for specificresistance have been used in commercial barley varietiessince the first gene, Mlg, was introduced on a large scalein the 1930s in Germany (Wolfe and Schwarzbach,1978; Jørgensen, 1994; Wolfe and MacDermott, 1994).In the 20th century in Europe, more than 700 cultivarsof barley have been used with different combinations of36 alleles for race-specific resistance to powderymildew. However, 28 of these alleles are closely linkedor allelic, which limits the possible number of genecombinations in breeding new varieties (Czembor andGacek, 1990; Brown and Jørgensen, 1991; Jørgensen,1994; Wolfe and McDermott, 1994). All these geneswere successively overcome by the appearance ofpathotypes with matching virulence. These varieties hadto be discarded because they were far too disease sus-ceptible to be of any further value. This susceptibilitywas due to a host erosion of partial resistance duringbreeding for race-specific resistance (Vertifolia effect)(Vanderplank, 1982; Czembor and Gacek, 1990).

This study demonstrate the practical advantages ofpreserving the genetic diversity of barley in the form oflandraces. Among 92 investigated landraces from Mo-rocco, 41 (45%) showed resistance for E. graminis f.sp.hordei. However, only 6 (170-1-3, 172-3-2, 173-1-2,181-3-5, 201-3-2, 201-3-3) from 79 lines originatingfrom these landraces were resistant to all isolates used.These lines had resistance to all powdery mildew viru-lence genes prevalent in Europe. This conclusion isbased on the fact that isolates used in this experimenthad virulences corresponding to all major resistancegenes used in the past and currently in Europe. Takingthis into account, they should be used in breeding ofbarley as a new sources of resistance to powderymildew. The frequency of powdery mildew resistantlandraces (170, 172, 173, 181, 201) in the present study,



IHARnumber

Number of isolates that produced infection type(0, 1, 2, 3 or 4)

0 1 2 3 4 Total

163-2-1 00 2 16 0 05 23163-2-5 01 1 14 0 07 23166-3-1 02 4 13 0 04 23169-1-2 06 0 01 0 16 23169-2-1 10 0 01 0 12 23169-2-5 03 0 10 0 04 17170-1-3 04 0 13 0 00 17170-1-4 03 1 16 0 03 23170-2-2 04 2 06 0 05 17170-3-4 03 0 17 0 03 23170-5-5 00 1 16 0 06 23171-2-1 04 0 16 0 02 22172-1-4 08 2 05 0 02 17172-3-2 04 4 09 0 00 17172-3-5 05 0 14 0 04 23173-1-2 11 3 03 0 00 17174-1-4 02 0 16 0 05 23174-2-2 02 0 07 0 08 17174-3-2 04 1 08 0 04 17178-1-4 01 0 07 0 09 17178-3-1 00 1 12 0 04 17179-2-1 00 0 15 0 08 23181-3-5 04 1 18 0 00 23182-1-1 00 0 19 0 04 23182-2-1 00 0 18 0 05 23182-3-2 00 0 18 0 05 23182-4-3 00 0 18 0 05 23184-2-1 00 0 15 0 06 21184-2-2 00 3 15 0 05 23189-1-1 01 0 18 0 04 23189-2-1 00 0 19 0 03 22189-3-3 00 0 18 0 05 23189-3-4 01 1 11 0 04 17190-3-2 01 0 17 0 05 23198-1-3 02 0 16 0 05 23198-1-5 00 1 13 0 03 17199-1-3 00 1 14 0 02 17199-2-1 00 0 17 0 05 22201-2-2 00 1 14 0 02 17201-2-3 00 0 18 0 05 23201-3-2 01 8 08 0 00 17201-3-3 02 2 19 0 00 23202-1-1 01 2 13 0 01 17202-1-2 00 0 17 0 06 23202-2-1 03 0 15 0 05 23

Table 6. Infection types frequencies of 45 lines for isolates of E. graminis f.sp.hordei.

5.4 per cent, is similar to or higher than that assessed inother studies (Honecker, 1938; Nover and Lehmann,1973; Czembor, 1976; Czembor et al., 1979; Negassa,1985; Lehmann and von Bothmer, 1988; Leur et al.,1989; Czembor, 1996; Jørgensen and Jensen, 1997;Czembor, 1999; Czembor and Czembor, 1999a). Thismay be caused by using the various methods for screen-ings landraces for resistance.

Incorporating genes for resistance to powderymildew originated from landraces into a barley breed-ing program should be a relatively easier when mutantsor wild barley are used. A good example of this is theintroduction of Mlo resistance into modern Europeanbarley cultivars. All twenty five different mlo alleleswith the exception of mlo11 were obtained by mutagen-esis. However, almost all barley cultivars with Mlo resis-tance have the same allele mlo11 which originated fromthe Ethiopian landrace L92 (Jørgensen, 1992a, b, 1994;Pickering et al., 1995). Furthermore undesirable agro-nomic traits that are usually derived from wild relativesdo not have to be bred out when using landraces as asource of powdery mildew resistance. Using barley lan-draces in breeding programs has also another advan-tage, which is the incorporation of desirable agronomictraits e.g. good adaptation to dry land conditions (Cec-carelli et al., 1987, 1991, 1995; Yahyaoui et al., 1996;Lakew et al., 1997).

Morocco is characterized by contrasts in its naturalconditions due to the transitional location between theMediterranean winter-rain zone and the Sahara desert(Perrino et al., 1986). This is reflected in very diverseplant material including barley obtained on germplasmcollection missions. Collecting missions in Morocco arehighly recommended because barley landraces in thiscountry are subject to genetic erosion due to droughtand desertification (Perrino et al., 1986; Damania, 1988;Tazi et al., 1989; Zine Elabidine et al., 1995). Barley isone of the most important cereal crops in the NorthAfrica including Morocco. It is grown as landraces inmarginal, low-input, drought-stressed environmentsboth for grain and straw (Ceccarelli et al., 1987, 1995;Czembor, 1996). It is presumed that they survive thefluctuations of biotic and abiotic stresses because oftheir high level of heterogeneity (Demissie and Bjørn-stad, 1996; Yitbarek et al., 1998). This was confirmed inthe present study by the fact that six landraces (about15%) were heterogeneous for mildew reaction. Thispercentage of observed powdery mildew resistance het-erogeneity of barley landraces is similar to or lower thanthat described in other studies (Nover and Lehmann,1973; Czembor, 1996, 1999; Czembor and Czembor,1999a).

In the farming system which uses landraces, pow-

dery mildew rarely develops to levels that significantlydamage the yield. This has been attributed both to thestabilizing effect of the genetic heterogeneity within thelandraces and to the presence of resistance sufficient tocontrol the limited disease development (Leur et al.,1989; Andrivon and Vallavielle-Pope, 1992). This wasconfirmed in this study. The most frequently observedscore in tested lines was 2 (65.0%) and 36 lines(80.0%) showed this reaction for inoculation with morethan 50% isolates used. This is different from the resis-tance reaction conferred by most powdery mildew re-sistance genes used in Europe which confer mostly re-action type 0 and 1 (Brown and Jørgensen, 1991; Jensenet al., 1992; Jørgensen, 1992a; Jørgensen, 1994; Czem-bor and Czembor, 1998, 1999b). In most selected lines(83.3%) the presence of unknown genes alone or incombination with specific ones were detected. Amongspecific resistance alleles the most common was alleleMlat which was postulated in 20 (44.4%) tested lines.This is in agreement with the fact that virulence to Mlatis very common in the Moroccan mildew populationand that Mlat resistance gene was originally describedfrom western North Africa (Caddel, 1976; Jørgensen,1994; Yahyaoui et al., 1997). The presence of a highnumber of unknown genes in barley landraces is inagreement with findings in other studies (Honecker,1938; Nover and Lehmann, 1973; Czembor, 1976;Czembor et al., 1979; Negassa, 1985; Lehmann and vonBothmer, 1988; Leur et al., 1989; Czembor, 1996; Jør-gensen and Jensen, 1997; Czembor, 1999; Czembor andCzembor, 1999a).

Crucial to the efficiency of breeding for resistance isthe durability of the resistance genes. It may be in-creased by using many different strategies for deployingresistance genes in barley. Most common of thesestrategies are: multiline cultivars, combining differentresistance genes into one cultivar and deploying manycultivars with different resistance genes in space (e.g.cultivar mixtures) or time (winter versus spring barley)(Jørgensen, 1983; Jørgensen, 1994; Czembor andGacek, 1995; Gacek, 1996). In last twenty years, newsources of resistance to powdery mildew were found inbarley landraces and wild barley. New sources of resis-tance, including sources described in this study, may beused by barley breeders in new cultivars employing dif-ferent strategies (Wolfe, 1984; Jørgensen, 1994; Jør-gensen and Jensen, 1997).

Determination of powdery mildew resistance genesbased on tests performed on seedlings is effective andsufficient for the needs of breeders and pathologists(Jørgensen, 1981; Brown and Jørgensen, 1991; Jensen etal., 1992; Jensen and Jørgensen, 1992a; Czembor andCzembor, 1998, 1999b). Generally, confirmation of re-


sistance composition can only be established by a testfor allelism through crosses and backcrosses among ap-propriate hosts (Czembor, 1996; Heitefuss et al., 1997).Also different levels of partial resistance in tested linesmay influence conclusions concerning the postulatedpresence of specific resistance genes (Jørgensen, 1994;Czembor, 1996).

This study confirmed the findings of other investiga-tors that many barley landraces possess mildew resis-tance genes different from genes present in cultivatedvarieties (Honecker, 1938; Nover and Lehmann, 1973;Czembor, 1976; Czembor et al., 1979; ; Negassa, 1985;Lehmann and von Bothmer, 1988; Leur et al., 1989;Czembor, 1996; Jørgensen and Jensen, 1997; Czembor,1999; Czembor and Czembor, 1999a). New effectivesources of resistance described in this study may in-crease the diversity of the powdery mildew resistancegenes present in barley cultivars in Europe.

ACKNOWLEDGEMENTS

The author thanks Dr. J. Valkoun (InternationalCenter for Agricultural Research in the Dry Areas –ICARDA, Aleppo, Syria) for providing seed samples ofbarley landraces from Libya, Dr. H.J. Schaerer(Edigenossische Technische Hochschule – ETH,Zurich, Switzerland) for the powdery mildew isolatesand Dr. L. Munk (Royal Agricultural and VeterinaryUniversity, Copenhagen, Denmark) for the near-iso-genic lines of Pallas.

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Received 10 January 2000Accepted 30 May 2000

Sources of powdery mildew resistance in barley landraces from morocco

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